Yesterday was the seventh chapter of my continuing education series at Stanford entitled "The Science of Longevity." My topic was more specifically focused on the aging brain. The context really goes back to a paper that I wrote 30 years ago entitled "Physical Exercise as an Evolutionary Force." (1)
In that article, I made the suggestion that the reason the human brain grew so actively in evolutionary terms was secondary to the fact that we became hunter-gatherers. Five million years ago we emerged from the jungle where our cousins, the chimps, still reside and their brains are the same size as then. Ours on the other hand have tripled in size. It is my conjecture that the reason that this happened was because as hunter-gatherers we chased our food or were chased for food until our survival was assured. This Paleolithic heritage resides between our ears today.
As a result of this early interest I have consecutively looked out for other story pieces that involve the effect of exercise on the brain. I have been restrained in my full enthusiasm until an article by Robert Dustman emerged a few years ago. (2) In it he showed how a group of older people's IQ went up when they exercised. This opened the door to a cascade of current work most particularly championed by Arthur Kramer of the University of Illinois and Carl Cottman of UC Irvine. My interest in movement and the brain grew.
Along the way I discovered the story of the sea squirt, an otherwise inconsequential maritime creature, found all over the world. Early in its life course it is free swimming and derives its foodstuffs from that which it can catch. However in midlife it attaches to a firm surface such as a coral head or a wharf pier. Consequently its nutritive choices change. To sustain itself it simply ingests the circulating ocean, and its differing caloric options such as plankton. As a result of this different feeding strategy it is no longer necessary to have a primitive brain to coordinate movement. The sea squirt turns around and eats its brain. Why have a brain if it is not necessary?
My reflection of this early chapter seems to indicate that as we humans seem to be moving less, we stop using our brains and our IQs suffer as a result. It is recognized that predator's brains are bigger than prey size. Domesticated animals have smaller brains than their wild cousins. Neanderthals had bigger brains than we do and were more physically active.
So there are multiple connections between exercise and brain size. I wonder if our current high-tech lifestyles are neglecting our legs, so that they are becoming vestigial.
So as we age I encourage us not to become sea squirts and keep moving. Move and keep your brain cells active to sustain your movement. If not maybe our legs will become relics and subsequently our brains as well.
What will be left of Homo sapiens if this doomsday scenario is played out?
1) Bortz, W. Exercise as an Evolutionary Force. J. Human Evolution 1985;14:145-155.
2) Dustman R. et al Aerobic Exercise Training and Improved Neuropsychological Function of Older Adults. Neurobiol Aging 1984 ;5:35-46.
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